Curtain for focal plane shutters



Dec. 14, 1948. 1 W DOYLE ET AL 2,456,052

CURTAIN FOR FOCAL PLANE SHUTTERS Filed Nov. 2, 1944 ATTO NEYS PatentedDec. 14, i948 UNITED STATES PATENT i OFFICE CURTAIN FOR FOCAL PLANESHUTTERS `Irving W. Doyle, Massapequa, and Carl V. Johnson, Kew Gardens,N. Y., assignors to Fairchild Camera and Instrument Corporation,Jamaica, N. Y., a corporation of Delaware Application November 2, 1944,Serial No. 561,556

3 Claims. 1

This invention relates to a curtain for a focal plane shutter.

As fixed slit focal plane shutters are capable of speeds in excess of athousandth of a second, their curtains must be capable of withstandingsubstantial stresses and forces to which they are subjected throughout acomplete cycle of operation. During the winding portion of the cycle,the full bias of the shutter spring is exerted on the curtain which, forthe sake of manufacturing expediency, is customarily made in two partsjoined together at the slit. When an exposure is made at high speed, thefull force of the spring is suddenly exerted on the curtain so as tosweep its slit across the focal plane. Although the curtain and itsassociated parts are relatively light in Weight, they have, however,Sufiicient inertia and gain sui'licient momentum, to cause undesirableexposure conditions. These conditions often result in improperly exposednegatives, particularly in the case of aerial photography, where in manycases extreme accuracy of reproduction is prerequisite.

Thus, if the width of the curtain slit varies during the exposure, thenegative is not uniformly exposed. inasmuch as the curtain slit iscustomarily formed by spaced relatively rigid strips of metal or thelike, these strips, because of their necessary light weight, arecharacterized by a certain amount of resiliency. Thus when the curtain,and accordingly the strips, move at high speed across the focal plane,the force of the shutter spring` may be transmitted through the curtainto one or both of the slit forming strips, thereby causing relativemovement between the strips during their exposure movement.

It is accordingly among the objects of this invention to provide acurtain for a focal plane shutter which, While simple, inexpensive andrugged in construction, yet overcomes the above disadvantages inaddition to others in an eilicient and practical manner.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts, as will beexemplified in the structure to be hereinafter described, and the scopeof the application of which will be indicated in the following claims.

In the drawing, wherein there is shown one form of the invention,

Figure 1 is a top plan view of the shutter with a portion broken away toshow a driving spring;

Figure 2 is a fragmentary top plan view of one of the shutter curtains;

Figure 3 is a substantially enlarged section taken along the line 3 3 ofFigure 1; and

Figure 4 is a substantially enlarged section taken along the line 4--4of Figure 1.

Similar reference characters refer to similar parts throughout thevarious views of the drawing.

In Figure l, a shutter is generally indicated at Il! and includes a pairof curtains II and I2, joined together at their ends which are spaced asuitable amount to provide an exposing slit I3. The opposite ends ofcurtains II and I2 are secured to rollers I4 and I5, one or the other ofwhich may include a conventional operating spring Ida which, when theshutter is released for operation, draws slit I3 across the focal planeaperture which lies between rollers I4 and I5.

Curtains I I and I2 are identical in all respects, and accordingly forbrevity we have shown in Figure 2 curtain I2. This curtain may be formedof any suitable opaque material, preferably a finely woven fabric whichmay be suitably treated to assure complete opacity. At the slit formingend of the curtain are a pair of tabs I6 and I'I by which curtain I2 isattached to curtain I I (Figure 1) in a manner to be hereinafterdescribed, to form slit I 3.

Referring back to Figure 2, the fabric between tabs I and II is slit asat 4U and 4I and is cut on a radius to provide a curved end portion I8to which is fastened a metal strip I 9. Strip I9 is U-shaped in crosssection and accordingly, as may be seen in Figure 4, comprises top andbottom flaps 20 and 2I, and a bight 22. The ends of strip I 9 (Figure 1)are so formed as to provide spaced attaching ears as, for example, ears23 and 24 (Figure 3), through which a rivet 25 extends to fasten the endof the strip to curtain tab Il of curtain I2, as well as curtain tab ISaof curtain II. The other end of slit strip I 9 (Figure 1) is similarlyattached to the other overlying tabs of curtains II and I2. The portionof strip I9 between its ends has disposed therewithin the curved edge I8(Figure 4) of curtain I2, which may be wrapped around a small rod 26which lies Within the bight 22 of the strip` When this curved edge ofthe curtain is installed about rod 26 Within the strip, the centralportion of the curtain is dra-wn away from the strip, while the ends ofthe curtain edge are held so that loose folds 21 (Figure 1) of thecurtain fabric are formed centrally thereof. The edge of the curtain maybe secured within strip I9 in any suitable fashion, as by cementing thefabric therewithin.

attacca Curtain I is similarly attached to a strip 28, the ends of whichare fastened to the curtain tabs in the same manner as describedhereinabove With respect to the joint shown in Figure 3. Thus theoverlying curtain tabs 16a and I'I are held against separation by tworivets 25 (Figure l) and the J'oint thus formed has stitched theretooverlying and underlying strips Eli and dll (Figure 3) of any suitablematerial, these strips being stitched to the curtain tabs as shown at 3lin Figure 1.

It Will now appear that the two curtains I l and l2 are securelyfastened together at the ends of slit I3, and also that the strips itand 23 which form slit i3 are fastened to the curtains in accu# ratelydimensioned spaced relationship, wherein they are held substantiallyimmovable relative to one another by reason of the nature of theirattachment to the curtains, and. by reason of their inherent substantialrigidity resulting from their U-s'hap'ed cross section, as well as therods, such as rod 26 (Figure 4) lying in the bight of each; Curtain Ilis, of course, fastened to strip 28 in thesame manner as described withrespect to curtain I2 and strip IS, so that loose folds 32 of materialare formed at the central portion of the curtain adj acent the edgethereof.

Wln curtains i i and i2 are mounted on rollers I 4 and I5, the shutteroperating spring in one of the rollers draws the two curtains taut sothat they lie llat adjacent the focal plane. Through the provision ofthe loose portions or folds 21 and 3,2 vin the curtains the tension ofthe shutter spring is to a substantial extent absorbed by the fabric ofthe curtains before being exerted on the central portions of strips i@and 28. Otherwise, the spring bias would bow the central portions of testrips away from one another, thus imparting to the opposite edges ofslit i3 a curvature rendering the slit width non-uniform. By the sametoken, the sudden pressure of the shutter spring on the curtain when anexposure is made is substantially absorbed by these loose curtainportions, with the result that there is little or no relative movementbetween the slit forming strips length of said curtain While motionlessat its longitudinal center line being greater than the length of saidcurtain along lines spaced transversely of its center line, the greaterlength of said curtain along its longitudinal center line being c1jeatedthrough the v provisiQm of a surplus ofniaterial adjacent to andintending away from the slit edge of the curtain where it is attached tox said strip.

2. A shutter curtain according to claim 1 wherein` the slit formingstrip comprises a rod extending transversely of the curtain and havingwrapped tlier'e'abdiittl'e leading edge of said curtain, said leadingedge being arcuate inthe directionof its r'noveincnt during exposureoperation, said slit forming strip also including an element extendingtransversely of the curtain and embracing said rod and those portions ofthe leading edge of the curtain adjacent to the rod, said arcuatecurtainuedgebeing so disposed in relation to a straight edg of saidle'nient as' to be substantially parallelthereto, whereby there iscreated a surplus 4of curtain niaterialadjacent said slit orniirig stripalong the central portions thereof.

3. a fof' plane, shutter curtain, in conbinatiori a relativelyrigid'straight slit Aforming strip, a 'cloth curtain nieinbr having slitand roller attaching edges, and means for attaching the slit edge o'fsaid curtain ineinbc to said strip, said roller attaching curtain edgebeing parallel to said strip, the length of said curtain While niotionls being "g'reateialong its longitudinal center line than the length thcurtain along lines spaced transversely of its center line whereby thereare ,c ated loosefolds of curtain fabric between said slit and ille'rattaching edges.

IRVING W. DOYLE. CARL V. JOHNSON.

REFERENCES CITED rlhe following references are of record in the le ofthis patent:

UNITEl STATES PATENTS' Number. Name Date 504,425 Schramm Sept. 5, 1893741,193 Br'sum oct. 13, 1903 .3u '792,361 Stocoum et al June 13, 1905arraigo ruimer ;g l Feb. 5, 1907 2,133,011 Black Oct. 11, 1938 FOREIGNPATENTs ff Number. Country., Date 14,839 Great Britain 1893 308,592Germany July l2, 1919

